Incident Overview
On 19 March 2020 at 11:23:33 local time, a serious incident involving a near collision occurred during final approach to runway 23 at Langenthal Airfield (LSPL), Switzerland. The two aircraft involved were a Robin DR 400/180 R (registration HB-KBP) and a Votec 322 (registration HB-YLC). The minimum separation between them was approximately 80 meters horizontally and 10 meters vertically. The event was classified as an ICAO Airprox Category A. No air traffic control was involved; the airspace was Class G.
Aircraft and Pilots
Aircraft 1 (HB-KBP) was a Robin DR 400/180 R owned and operated by Segelfluggruppe Oberaargau. The pilot, a Swiss national born in 1952, held a Private Pilot Licence (PPL(A)) issued by EASA. He had logged 1,565 total flight hours, including 1 hour in the last 90 days, with 91 hours on type (1 hour in the last 90 days). The aircraft was equipped with a transponder and a Flarm collision warning device; the transponder was not switched on during the incident.
Aircraft 2 (HB-YLC) was a Votec 322 owned by a private individual and operated by Flying League Langenthal. The pilot, a Swiss national born in 1949, also held a PPL(A) from EASA. He had 1,857 total flight hours, 1 hour in the last 90 days, and 70 hours on type (0:32 hours in the last 90 days). The aircraft was equipped with a transponder; a Powerflarm had been purchased but not yet installed.
Sequence of Events
The pilot of HB-YLC departed Grenchen (LSZG) after a touch-and-go and climbed back to Langenthal. He reported on the airfield frequency in the north sector at approximately 3,100 ft AMSL.
Around 11:10 local time, the pilot of HB-KBP departed Langenthal runway 23 towing a glider (HB-3429). After reaching about 4,700 ft AMSL, the glider released, and the Robin pilot returned to Langenthal, planning a right base for runway 23—a non-standard approach used by the glider group for noise abatement. He made a blind call on the frequency.
Overflying the airfield at about 3,000 ft AMSL, the HB-YLC pilot saw a Robin on the taxiway and a glider on the ground, assumed the towing operation would wait, and entered a left downwind, descending slightly. He made another position report, heard by the HB-KBP pilot.
The HB-KBP pilot then broadcast his intention: "Schloss Thunstetten, right hand base 23" at about 2,400 ft AMSL. While turning final, he saw the Votec turning left base at a higher altitude than typical. The HB-YLC pilot turned final at around 2,900 ft AMSL and reduced power for a left slip (glissade) power-off approach. The HB-KBP pilot, assuming the Votec pilot had seen him and would continue toward the Jura, continued his approach, reducing speed to about 100 km/h.
Approximately 200 meters from the runway threshold, as HB-KBP initiated the flare, HB-YLC overtook and touched down ahead. The HB-KBP pilot felt wake turbulence from the Votec, applied full power, and executed a go-around. After a left-hand circuit, he landed without further incident.
Findings
Investigators determined that the approach speeds differed significantly: the Robin's final approach speed at maximum landing weight was 62 kt (115 km/h), while the Votec's was about 100 MPH (161 km/h). No technical malfunctions were identified.
The HB-YLC pilot's headset had a broken right earpiece. Due to engine noise, he could not clearly hear the HB-KBP's position reports—a factor that contributed to the incident. He never saw the lower Robin because he was in a slip during approach.
The standard traffic pattern for runway 23 at Langenthal is a left-hand circuit. The right base used by the glider group is not published in the VFR Manual. Both pilots were aware of this non-standard approach.
Weather
Weather conditions were sunny with light wind (270°/4 kt), visibility 8 km, haze over the Swiss Plateau, and clouds at 1–2/8 coverage at 5,400 ft AMSL. Temperature was 14°C, dew point 9°C, and QNH was 1025 hPa. Conditions were suitable for visual flight and did not influence the incident.